kilodawg

Juha,

I agree with techman1's comments in principle. While I respect the learned opinions of experts who have posted here. I do not know how seriously this problem has ever been investigated by outside (as in independent) software/electrical engineers. I would love to hear the analysis/opinions from a competent, independent third party review..

911Dave

Maybe we can convince ltc (aka SAI Circuit-Bypass-Man) to rig up a bunch of $10 immobilizer-busters.

Seriously, look into rebuilding your module rather than replacing it. Loren rebuilds control modules of all kinds I believe. That is, if your module is failing. I'm still betting on a loose wire connection.

kilodawg

I'm believing and hoping the same.

I looked at Loren's site but while lots of rebuilt units are listed there I didn't see immobilizers.

bobt993

Ralph,

A couple of things to try. I ran into similar issues on my 96 993.

1. Remove all the units from the car and take them apart ( under passenger and driver seats). Clean the pin connections on the ECU and remove any potential moisture deposits from the board using electronics parts spray cleaner. You must also really clean well the plastic insulator card that is on the circuit trace side of the ECU. Clean the immobilizer and doorlock boards also.

You can bypass the starter cut off at the relay in the fuse box. (there are threads on this, simple jumper under the relay). The 96 ECU needs the "unlock code" to function. You may be able to borrow a de-programmed computer to test if this indeed is your problem. Most of the 97-98 computers are actually shipped to Germany to be programmed. Also clean the contacts on your key fob and make sure that the battery clips have good tension against the small battery. I have intermittent contact cause this problem too.

Last option install Motec...............................

It is very common for moisture or high humidity to cause the problem you are having and very often cleaning the boards will correct this.

Carlos993

Bob, just to be clear, installing Motec will eliminate the immobiiizer problem, even for a 96? Thanks in advance.

Juha G

It will elimanate the ECU part of the immobilizer. The starter relay cut-off can be eliminated as posted above or as I did. (soldered a jump wire on the immobilizer)
The good thing about installing a Motec is that you can optimize your fuel&ignition maps. I got +35hp and +50Nm by doing this.
You can also make a adaptor harness to make it 100% plug'n'play like I did.
I can send you the info you decide to go ahead with the Motec.
Here's my thread about the Motec installation: https://rennlist.com/forums/993-foru...ml#post7996140

bobt993

Yes, you need to add a jumper to the starter relay circuit. My car was converted to race so I cannot tell you what to do with the door locks. I think the keyless entry still works independently as does the ABS system. I actually have a conversion box for the factory harness that makes the Motec unit a plug in for the 993. ( You only need to run a Lambda O2 wire to the exhaust and convert the Mas airflow over to a barro sensor. 9mm and Racetek make the conversion boxes.

Lorenfb

"Just trying to understand what statements that have been made are accurate or not."

Based on evaluations of the '96 993 DME ECM, that ECM used a microprocessor
which had the instruction codes for its program encoded into a 'masked' ROM
(read-only-memory) at chip production time versus the later 993s which had
a flashable memory (like an SD card) which is changeable. To make any
program changes to the '96 ECM, the microprocessor must be removed and
replaced by a 'biggy-back' microprocessor and another memory chip,
i.e. not a simple task for long term reliability.

Having been involved with many 993s while helping Porsche dealers and
independents in SoCal, very few (if any) have had immobilizer problems.
The exception is water damage or over-voltage from battery chargers.

Before assuming a bad immobilizer:
1. Check all of its powers and grounds.
2. Check that the ignition switch signals (critical) are there,
i.e. key in/out & #15/#30.
3. That the code signal on the K-Line is getting to the ECM
via and O-scope.
4. That the ECM has all of its powers (2 #15, 1 #30) and grounds.
5. If the immobilizer can command the alarm unit to lock/unlock the
doors and allows the engine to crank, then the immobilizer just lacks
proper communications with the ECM.

Bottom line: Without proper diagnosis, an assumption of a bad immobilizer
is a potential waste of time and money.

kilodawg

Thanks Loren!

e9stibi

I am quite late to the party but wanted to add some guidance that I recently documented when I troubleshot a starting issue. I agree with some of the posters that proper analysis should be made before jumping on replacing parts, in particular electronic boxes:

0. Swap DME relay with the spare I had in the glove box. Car did not give a single sound while starting -> rule out DME relay issue at the moment
1. Battery voltage 12.8 V and I switched it with the one from my second (starting) 993. Still no cranking or klicking from the solenoid -> battery ok
2. All connection at battery tight and mass band in trunk "looks like new" -> ruled out issues here at the moment
3. Switched Starter relay (R61) with a similar relay that knowingly works (e.g. horn that is easy to test). car still "dead while starting -> starter relay R61 ok
4. Pull starter relay R 61 and do the following measurements:
4.a Check pin 86 for 12V. This is the 12V from the immobilizer to the starter relay coil that acts as an interlock to start the car. In my case I got the 12 V when I opened the car properly and turned the ignition on within the required time. -> immobilizer ruled out as an issue
4.b. Check pin 85 for proper mass signal (resistance measurement against mass). MJ 97 and later have a clutch switch that provides the mass to the starter coil switch. I measured "0 Ohm" with depressed clutch -> ruled out clutch switch

The previous measurements confirmed that the starter relay coil gets the proper supply. No to the power side of R61

4.c. Check pin 30 for 12V with the ignition switch turned to position 3 (start position to crank). I measured 12 V. -> ruled out ignition switch issue

The previous measurement confirmed that the power side of the R61 gets the proper signal too (12V). This all ruled out any relay related issues "in the trunk". I than moved to the starter and its connections as I assumed that an issue with the cable that provides the switched 12 V from starter relay power side to the starter solenoid is not likely.

5. Checked starter for tight and clean connections. Need to include the mass connection at the chassis side -> everthing was thight and clean like new -> IT MUST BE THE STARTER

6. Replaced starter -> car starts as it is suppsed to start!

Bottomline is as Steve already said: Root causes can be multiple and proper and "cheap" diagnosis before replacing expensive parts like Immobilizer unit can safe both time and money.

Here is the list of potential issues again that can lead to a car not starting "from the electrical side" and I am sure there is more when you include general "cable issues" between working components.

1. DME relay
2. Battery
3. Battery connections
4. Starter Relay R61
5. Immobilizer Unit / maybe key fob if you are lucky
6. Clutch switch (for MJ 97 and 98)
7. Ignition switch
8. Connections to starter
9. starter itself

Good Luck!

911Dave

10. Bad solenoid

Great post e9stibi!

kilodawg

Excellent write up e9stibi. I'm sure my wrench is going down a similar investigative path now....

kilodawg

Final update (don't you hate it when people don't closeout troubleshooting threads)

The problem was NOT the immobilizer itself but it was corrosion on a couple of pins between the ECU and the immobilizer as well as one in the fuse/relay box in the trunk. While he was at it my wrench checked the wiring and other pins for my alarm which was also intermittent. That's all cleared up as well now. So complete functionality of the immobilizer and alarm system has been restored without requiring the replacement of any parts.

Again, I never cease to be impressed by the quality of work that Lou at Aerodynamics in Port Orange Florida brings to the task. Many thanks Lou!!!